Recent advancements in display technology are beginning to allow for an extended range of color, luminance and contrast to be displayed.
Technologies allowing for extensions in luminance or brightness range of image content are known as high dynamic range imaging (HDR). HDR technologies focus on capturing, processing and displaying content of a wider dynamic range.
Although a number of HDR display devices have appeared, and image cameras capable of capturing images with an increased dynamic range are being developed, there is still very limited HDR content available. While recent developments promise native capture of HDR content in the near future, they do not address existing content.
To prepare conventional (hereon referred to as LDR for low dynamic range) content for HDR display devices, reverse or inverse tone mapping operators (iTMO) can be employed. Such algorithms process at least the luminance information of colors in the image content with the aim of better recovering or recreating the original scene. Typically, iTMOs take a conventional (i.e. LDR) image as input, at least expand the luminance range of the colors of this image in a global manner, and subsequently process highlights or bright regions locally to enhance the HDR appearance of colors in the image.
Typically, HDR imaging is defined by an extension in dynamic range between dark and bright values of luminance of colors combined with an increase in the number of quantization steps. To achieve more extreme increases in dynamic range, many methods combine a global expansion with local processing steps that enhance the appearance of highlights and other bright regions of images.
To enhance bright local features in an image, it is known to create a luminance expansion map, such that each pixel of the image can be associated with an expansion value to apply to the luminance of this pixel. In the simplest case, clipped regions in the image can be detected and then expanded using a steeper expansion curve, however such a solution does not offer sufficient control over the appearance of the image.
When dealing with sequence of images, prior art mostly referring to Inverse Tone Mapping does not generally take into account the temporal aspect. Sequences of images can be processed on a frame basis with different strategies:                Combination of local and global expansion of luminance range following different functions: inverse sigmoid, linear or piecewise linear.        Spatial expansion of luminance range on a pixel basis, relying on a spatial filtered version of the original LDR frame. This spatial filtered version may be a low pass version of bright areas of the LDR image. Edges can be preserved in this filtered version to ensure consistent luminance expansion.        
Concerning temporal artefacts or issues, methods that are disclosed in Prior Art do not really apply a processing for ensuring a temporal stability, but rather follow original luminance variation (locally and globally) that intrinsically induces a temporal stability in the expansion, but do not guarantee it.
There is a need for a novel iTMO, which aims to enhance the temporal stability and the temporal consistency of inverse tone mapped sequences of images.